The document discusses sex determination in multicellular organisms, highlighting primary and secondary sexual differentiation and the role of sex chromosomes, specifically the X and Y chromosomes in humans. It explains conditions such as Klinefelter syndrome and Turner syndrome, which result from atypical chromosome patterns affecting sexual development. The document emphasizes that males have one X and one Y chromosome, while females have two X chromosomes, detailing the genetic implications of these differences.

1. Copyright © 2009 Pearson Education, Inc.
Sex Determination
and
Sex Chromosomes

2. Copyright © 2009 Pearson Education, Inc.
Objectives:
• Discuss how sex is
determined

3. Copyright © 2009 Pearson Education, Inc.

4. Copyright © 2009 Pearson Education, Inc.

5. Copyright © 2009 Pearson Education, Inc.

6. Copyright © 2009 Pearson Education, Inc.

7. Copyright © 2009 Pearson Education, Inc.

8. Copyright © 2009 Pearson Education, Inc.

9. Copyright © 2009 Pearson Education, Inc.
In multicellular organisms, it is important
to distinguish between:
• primary sexual differentiation
•involves only the gonads where
gametes are produced
• secondary sexual differentiation
•involves the overall appearance of
the organism

10. Copyright © 2009 Pearson Education, Inc. Figure 7.2

11. Copyright © 2009 Pearson Education, Inc.
The Y Chromosome Determines
Maleness in Humans
• Human karyotype revealed that
one pair of chromosomes differs in
males and females:
• females have two X
chromosomes
• males have one X and one Y
chromosome

12. Copyright © 2009 Pearson Education, Inc. Figure 7.6
Normal Human Karyotypes

13. Copyright © 2009 Pearson Education, Inc.
• Persons with
Klinefelter
syndrome have:
• male genitalia
• more than one
X chromosome
(usually XXY, or
a 47,XXY
karyotype) http://all4freehere.com/2009/07/what-is-klinefelters-syndrome/

14. Copyright © 2009 Pearson Education, Inc. Figure 7.7a

15. Copyright © 2009 Pearson Education, Inc.
• Persons with
Turner syndrome
usually have:
• a single X
chromosome
• no Y
chromosome
(45,X karyotype)
• female genitalia
http://www.lucinafoundation.org/assets/turner-syndrome.jpg

16. Copyright © 2009 Pearson Education, Inc. Figure 7.7b

17. Copyright © 2009 Pearson Education, Inc.
• 47, XXX – Trisomy X
• 3 X chromosomes along with a
normal set of autosomes results in
female differentiation.
• Usually normal
• In other cases, underdeveloped
secondary sex characteristics,
sterility, and mental retardation may
occur.

18. Copyright © 2009 Pearson Education, Inc.
47, XYY –
Jacobs
Syndrome
• Males are
usually over 6
feet tall.
https://slideplayer.com/slide/16570608/

19. Copyright © 2009 Pearson Education, Inc.
• The Y
chromosome
contains far
fewer genes than
the X
chromosome.
http://blogs.discovermagazine.com/notrocketscience/files/2010/07/XY.jpg

20. Copyright © 2009 Pearson Education, Inc.
• Y chromosome
contains:
• the male-
specific region
of the Y (MSY)
• a sex-
determining
region of the Y
(SRY)
Section 7.3

21. Copyright © 2009 Pearson Education, Inc.
The Ratio of Males to Females
in Humans is not 1.0
• Primary sex ratio reflects the
proportion of males to females
conceived in a population.
• Secondary sex ratio reflects
the proportion of each sex that
is born.
http://partywarehouse.co.nz/zen/images

22. Copyright © 2009 Pearson Education, Inc.
Key concepts
• Males have 44 body chromosomes and
two sex chromosomes X and Y. The
males determine the sex of their
children. Females have 44 body
chromosomes and two sex
chromosomes, both X. The total number
in each cell of individual is 46. These
chromosomes contain the genes, which
are the factors of heredity.
http://partywarehouse.co.nz/zen/images